1. Field of the Invention
The present invention relates to a data buffering device having a data buffer which permits plural sets of data to be stored one set by one therein such that each set of data is stored in a first storage area as the first storage area is advanced from one area to another over a predetermined number of storage areas of the buffer in a predetermined sequence, and which permits the stored sets of data to be read out one set by one therefrom in the same sequence such that each set of data is read out from a second storage area as the second storage area is advanced from one area to another over the storage areas in the sequence. The present invention particularly relates to improving the processing rate or speed of at least one of data storage in the buffer and data reading from the buffer.
2. Related Art Statement
The data buffering device as indicated above is used for, for example, a printer which is connected to a print data supply such as a personal computer or a word processor and serves as an output unit of the data supply. The data supply supplies print data such as code data or vector data to the printer. The printer has processing means for converting the print data to dot data, and printing means for carrying out printing according to the dot data. More specifically, the data buffering device has a data buffer which permits plural sets of print data supplied from the data supply to be stored one set by one therein such that each set of data out of the supplied sets of data is stored in a first storage area as the first storage area is moved or advanced from one area to another over a predetermined number of storage areas of the buffer in a predetermined sequence, and which permits the stored sets of data to be read out one set by one therefrom in the same sequence such that each set of data out of the stored sets of data is read out from a second storage area as the second storage area is advanced from one area to another over the storage areas in the sequence. The print data read out from the data buffer is converted into dot data, and printing is carried out according to the dot data. Thus, the data buffering device assures that the printer carries out printing in a reliable manner even if a data storage in the buffer and a data reading from the buffer do not synchronize with each other, or even if processing speeds (or cycle times) of a data storage and a data reading do not match each other. These data buffering devices find various applications, other than use for printers, in which the above-described advantageous function thereof is required.
In a data buffering device, data storage in, or data reading from, a data buffer thereof is started from a head or leading storage area (or leading address) of the buffer and is advanced in a predetermined sequence to a last or trailing storage area (or trailing address) of the buffer. In other words, the above-indicated first or second storage area is advanced in the predetermined sequence from the leading address to the trailing address of the buffer. If the first or second storage area comes to the trailing address, then the area is required to return to the leading address so that data storage or reading can further be advanced from the leading address. Meanwhile, if the data buffer has no storage area which permits data storage therein, or no storage area which has data stored therein and permits data reading therefrom, it is not permissible to carry out data storage or reading on the buffer. Therefore, the data buffering device is required to have judgements-executing means for executing a return judgement whether or not it is necessary to return the first or second storage area from the trailing address of the buffer to the head address thereof, and executing a possibility judgement whether or not the buffer has any storage area that permits data storage therein or data reading therefrom. Conventional data buffering devices are adapted to execute these return and possibility judgements each time a set of data is stored in, or read out from, the data buffer thereof.
Thus, the conventional data buffering devices suffer from the problem that a comparatively long time is needed for a data storage in the data buffer or a data reading from the buffer, that is, that the rate or speed of data storage or data reading is unsatisfactory.